The present application relates to a storage element having a storage layer for storing a magnetization state of a ferromagnetic layer as information, and a magnetization fixing layer in which a direction of magnetization is fixed, and adapted to change the direction of the magnetization of the storage layer by causing a current to flow through the storage layer, and a memory device including the same.
A high-density DRAM (Dynamic Random Access Memory) which operates at a high speed is generally used as a random access memory in an information apparatus such as a computer.
However, since the DRAM is a volatile memory in which when a power source is turned OFF, information stored therein is erased, a non-volatile memory is desired in which information stored therein is not erased.
Also, a magnetic random access memory (MRAM) for recording therein information in accordance with magnetization of a magnetic material attracts attention as a candidate of the non-volatile memory, and the development of the MRAM is advanced.
In the MRAM, currents are caused to flow through two kinds of address wirings (a word line and a bit line) approximately bisecting at right angles with each other, respectively. Also, magnetization of a magnetic layer of a magnetic storage element disposed at an intersection point between the two kinds of address wirings is reversed by current magnetic fields generated from the two kinds of address wirings, thereby recording information.
FIG. 8 is a schematic view (perspective view) showing a structure of a general MRAM.
A drain region 108, a source region 107, and a gate electrode 101 composing a selecting transistor for selecting corresponding one of memory cells are formed in a portion which is isolated from other portions by an isolation layer 102 of a semiconductor substrate 110 such as a silicon substrate.
In addition, a word line 105 which extends in a front-back direction in FIG. 8 is provided above the gate electrode 101.
The drain region 108 is formed which the right-hand and left-hand side selecting transistors in FIG. 8 hold in common. Also, a wiring 109 is connected to the drain region 108.
Also, a magnetic storage element 103 is disposed between a word line 105 and a bit line 106 disposed above the word line 105 so as to extend in a horizontal direction in FIG. 8. In this case, the magnetic storage element 103 has a storage layer a direction of whose magnetization is adapted to be reversed. Also, the magnetic storage element 103, for example, is composed of a magnetic tunnel junction element (MTJ element).
In addition, the magnetic storage element 103 is electrically connected to the source region 107 through a bypass line 111 extending in a horizontal direction, and a contact layer 104 extending in a vertical direction.
Currents are caused to flow through the word line 105 and the bit line 106, respectively, to apply a current magnetic field to the magnetic storage element 103. As a result, the direction of the magnetization of the storage layer of the magnetic storage element 103 is reversed, thereby making it possible to record information.
Also, for stably holding the recorded information in the magnetic memory such as the MRAM, it is necessary for the magnetic layer (storage layer) for recording therein the information to have a given coercive force.
On the other hand, for rewriting the recorded information, a certain amount of current needs to be caused to flow through the address line.
However, a sufficient amount of current comes to be unable to be caused to flow because the address line becomes thin in accordance with the scale down of the elements composing the MRAM.
Then, with regard to the structure with which the magnetization reversal can be made with the less current, a memory having a structure in which the magnetization reversal by spin injection is utilized attracts attention. This technique, for example, is described in Japanese Patent Laid-Open No. 2003-17782, U.S. Pat. No. 6,256,223, and Japanese Patent Laid-Open No. 2008-227388, and a Non-patent Document of PHYs. Rev. B, 54. 9353 (1996) and a Non-patent Document of J. Magn. Mat., 159, L1 (1996).
The magnetization reversal by the spin injection is such that an electron which passes through a magnetic material to be spin-polarized is injected to another magnetic material, thereby causing the magnetization reversal in another magnetic material.
For example, a current is caused to flow in a direction vertical to a film surface through a giant magnetoresistance effect element (GMR element) or a magnetic tunnel junction element (MTJ element), thereby making it possible to reverse a direction of magnetization of at least a part of a magnetic layer of such an element.
Also, the magnetization reversal by the spin injection has an advantage that even when the element is scaled down, the magnetization reversal can be realized without increasing the current.
FIGS. 9 and 10 are respectively schematic views of a memory device having a structure in which the magnetization reversal by the spin injection described above is utilized. Here, FIG. 9 is a perspective view, and FIG. 10 is a cross sectional view.
A drain region 58, a source region 57, and a gate electrode 51 composing a selecting transistor for selecting corresponding one of memory cells are formed in a portion which is isolated from other portions by an isolation layer 52 of a semiconductor substrate 60 such as a silicon substrate. Of these constituent elements, the gate electrode 51 serves as a word line as well which extends in a front-back direction in FIG. 9.
The drain region 58 is formed which the right-hand and left-hand side selecting transistors in FIG. 9 hold in common. Also, a wiring 59 is connected to the drain region 58.
Also, a storage element 53 is disposed between the source region 57 and a bit line 56 disposed above the source region 57 and extending in a horizontal direction in FIG. 9. In this case, the magnetic storage element 53 has a storage layer a direction of whose magnetization is adapted to be reversed by the spin injection.
Also, the magnetic storage element 53, for example, is composed of the magnetic tunnel junction element (MTJ element). The storage element 53 has two magnetic layers 61 and 62. Of the two magnetic layers 61 and 62, one magnetic layer is used as a magnetization fixing layer the direction of whose magnetization is fixed, and the other is used as a magnetization free layer a direction of whose magnetization is adapted to be changed, that is, a storage layer.
In addition, the storage element 53 is connected to the bit line 56 and the source region 57 through an upper contact layer 54 and a lower contact layer 54, respectively. As a result, a current is caused to flow through the storage element 53, and thus the direction of the magnetization of the storage layer can be reversed by the spin injection.
In the case of the memory device having such a structure as to utilize the magnetization reversal by such spin injection, the device structure can be simplified as compared with the general MRAM shown in FIG. 8. For this reason, the memory device concerned has an advantage as well that the density growth becomes possible.
In addition, utilization of the magnetization reversal by the spin injection provides an advantage that even when the scale down of the element is advanced, a write current is not increased as compared with the general MRAM in which the magnetization reversal is carried out by an external magnetic field.